`extension create`: Move Core plugin scaffolding generators from Core

[lasomethingsomething]

Move the existing plugin scaffolding from shopware/shopware/src/Core/Framework/Plugin/Command/Scaffolding into Shopware CLI.

The generators should be exposed individually instead of through the existing plugin:create questionnaire.

Compatibility: the minimum version for the full clean generator set is Shopware 6.7.13.0.

Generator review

Generator	Current Core command	Last relevant change	Treatment
AdminModuleGenerator	make:plugin:admin-module	2026-04-22 a5bc729c: en-GB/de-DE → en/de	additive
CommandGenerator	make:plugin:command	2026-07-27 42998569: XML → PHP registration	additive
ComposerGenerator	make:plugin:composer	2025-08-20 c35b1a97: composer/namespace handling	#1274 foundation
ConfigGenerator	make:plugin:config	2025-01-21 14370ace: annotation only	additive
CustomFieldsetGenerator	make:plugin:custom-fieldset	2026-06-24 cc226a48: installer/lifecycle → declarative custom-fields.xml	additive, >=6.7.13.0
EntityGenerator	make:plugin:entity	2026-08-12 daf7b4e6: preserve existing files/migrations	additive; port preservation semantics
EventSubscriberGenerator	make:plugin:event-subscriber	2026-07-27 42998569: XML → PHP	additive
GitignoreGenerator	make:plugin:gitignore	2025-10-06 f2e28d3c: add .gitignore	#1274 foundation
JavascriptPluginGenerator	make:plugin:javascript-plugin	2025-01-21 14370ace: annotation only	additive
PluginClassGenerator	make:plugin:plugin-class	2025-01-21 14370ace	#1274 foundation; don't port current lifecycle-heavy stub
ScheduledTaskGenerator	make:plugin:scheduled-task	2026-07-27 42998569: XML → PHP	additive
StoreApiRouteGenerator	make:plugin:store-api-route	2026-07-27 42998569: PHP services/routes	additive
StorefrontControllerGenerator	make:plugin:storefront-controller	2026-07-27 42998569: XML → PHP	additive
TestsGenerator	make:plugin:tests	2025-08-20 c35b1a97	needs decision: generated bootstrap uses addActivePlugins() / setForceInstallPlugins(true)
AddScaffoldConfigDefaultBehaviour / HasCommandOption / ScaffoldingGenerator	—	2025-01-21 14370ace	internal infrastructure

CustomFieldsetGenerator sets the compatibility floor: through 6.7.12.1 it generated an installer, service registration, lifecycle hooks and repository operations. cc226a48 replaced these with declarative Resources/config/custom-fields.xml.

The July XML → PHP changes do not raise the floor; PHP configuration is supported by 6.7.13. The August EntityGenerator preservation behavior is CLI-side safety and should be ported independently of the runtime target.

Do not copy the stub directory wholesale: plugin-class.stub still contains lifecycle hooks, and plugin-class-with-custom-fields.stub is obsolete for this ownership model.

Acceptance criteria / checks

• Additive generators are available individually through Shopware CLI.
• Full-generator compatibility is >=6.7.13.0; unsupported targets fail clearly.
• composer.json, .gitignore and a minimal plugin class stay in Create a minimal, valid plugin with extension create #1274 and are not exposed as post-create generators.
• Port current templates plus daf7b4e6 preservation/idempotency behavior.
• Existing files follow defined skip/append/fail semantics; user code is never overwritten and services.php / routes.php are not duplicated.
• Decide whether TestsGenerator's test-runtime lifecycle behavior is within the extension create: Consolidate plugin and theme creation and scaffolding in Shopware CLI #1255 boundary; otherwise exclude/redesign it.
• Interactive and non-interactive invocation produce equivalent artifacts for the same inputs.
• Intentional differences from Core are documented and tested.
• Implement telemetry (Grafana) so we can measure generator usage.
• Tests cover supported generator/version combinations.
• After migration, shopware-cli owns the migrated templates.